Vol 92, No 2 (2018)

The authors’ earlier works on the dielectric properties of different dialkyl sulfoxides and solutions of them are reviewed.

Enthalpies of the protonation of glycine in water‒dimethylsulfoxide (DMSO) mixed solvents are determined calorimetrically in the range of DMSO mole fractions of 0.0 to 0.9, at T = 298.15 K and an ionic strength μ = 0.3 (NaClO₄). It is established that the protonation of glycine becomes more exothermic with an increasing mole fraction of DMSO, and the enthalpies of resolvation of glycine and glycinium ions in water‒DMSO solvent mixtures are calculated. It is shown that the small changes in the enthalpy of protonation observed at low mole fractions of DMSO are caused by the contributions from the solvation of proton and protonated glycine cancelling each other out. The enthalpy term of the Gibbs energy of the reaction leading to the formation of glycinium ion is estimated along with the enthalpy of resolvation of the reacting species in the water‒DMSO mixed solvent.

The thermodynamic properties of amorphous polyphenylquinoxaline in the temperature range of 6 to 570 K are studied via precision adiabatic vacuum calorimetry and differential scanning calorimetry. The thermodynamic characteristics of glass transition are determined. Standard thermodynamic functions C^°_p, H°(T) − H°(0), S°(Т) − S°(0), and G°(T) − H°(0) in the range of T → 0 to 570 K and the standard entropy of formation at T = 298.15 K are calculated. The low-temperature (T ≤ 50 K) heat capacity is analyzed using a multifractal model for the processing of heat capacity, fractal dimension D values are determined, and conclusions on the topological structure of the compound are drawn.

The heat capacity of a first-generation carbosilane dendrimer with terminal phenylethyl groups as a function of temperature in the range from 6 to 520 K is studied for the first time via precision adiabatic vacuum calorimetry and differential scanning calorimetry. Physical transformations, such as low-temperature structural anomaly and glass transition are detected in the above-mentioned range of temperatures, and their standard thermodynamic characteristics are determined and analyzed. The standard thermodynamic functions of the studied dendrimer in the range of T → 0 to 520 K are calculated from the experimental data, as is the standard entropy in the devitrified state at T = 298.15 K. The standard thermodynamic characteristics of the carbosilane dendrimers studied in this work and earlier are compared.

Complex heterogeneous catalytic processes involving strongly chemisorbed particles (SCPs) are considered: syntheses of methanol, pyrocatechol, and diphenylamine and hydrogenation of CO and benzene. Nonstationary transformations of SCPs (CO and benzene) during continuous analysis of the gas phase are studied with mass spectrometric, flame ionization and thermal conductivity detectors. It is shown that the adsorption substitution reaction (ASR) proceeds before catalysis under typical conditions of these processes; in other words, the substitution reaction, rather than Langmuir adsorption equilibrium, determines the composition of reactive species on the catalyst surface. Consequently, ASRs and chemical transformations of SCPs must be considered for kinetic description of heterogeneous catalytic processes. It is shown that the ASRs allow us to describe these catalytic processes simply and adequately, and the obtained models can be used for the regulation and optimization of processes.

It is shown for toluene oxidation with nitrous oxide that modifying HZSM-5 zeolite with zinc oxide nanoparticles considerably improves the selectivity and yield of cresols. It is found that a 2% ZnO/HZSM-5 composite catalyst also exhibits enhanced and stable activity at high temperatures. For the o-cresol isomerization reaction, this modification of HZSM-5 zeolite greatly reduces the contribution from disproportionation and cracking reactions proceeding with formation of phenol, C₆–C₉ aromatic hydrocarbons, and xylenols. The regularities of their formation in the presence of the studied catalysts are determined using the results from thermodynamic calculations for the equilibrium concentrations of cresol isomers.

The mechanism and regioselectivity of cycloaddition reaction between diphenyl hydrazonoyl chloride and phenyl triflyl acetylene as an electron-deficient dipolarophyl in acetonitrile at room temperature are theoretically investigated using density functional theory and solvent polarized continuum model. Two general mechanism, concerted and stepwise mechanism, have been proposed for this reaction. Each mechanism has two different paths and two possible products. The activation energies of pathways were calculated using quantum mechanical approach and compared with each other. An excellent agreement was observed between the previously reported experimental work and the theoretical approaches for regioselectivity of this reaction.

The phase diagram of an ethylene glycol (EG)–hexamethylphosphorotriamide (HMPT) system is studied over two wide temperature intervals (+25°С…−90°С…+40°С) and (−150°С…+40°С) by means of differential scanning calorimetry using INTERTECH DSC Q100 and METTLER TA4000 DSC instruments (Switzerland) in the DSC30 mode with variable cooling/heating rates. Substantial overcooling of the liquid phase, a glass transition, and different types of interaction are observed in the system. No thermal effects are observed in intermediate range of concentrations during the slow cooling/heating processes, and the system remains liquid until the glass transition. The presence of such a metastable phase is attributed to a sharp rise in the viscosity of the system due to different kinds of interaction between the components. HMPT: 2EG and HMPT: EG compounds with crystallization temperatures of +5 and −0.5°С, respectively, are observed upon rapid cooling and slow heating. Changes in enthalpy are calculated for all of the observed thermal effects. The distinction from the phase diagram of H₂O–HMFT (literary data) is explained by the difference in the interactions between system components and by the structural differences between EG and H₂O.

The kinetics of crystalline iodine dissolution in ethanol at room temperature and 60°C is studied using the electronic absorption spectra of iodine solutions. Dissolution is shown to proceed for more than three months. It is found that the process begins with the formation of hydroiodic acid HI and is complete with the formation of I₃⁻ anions.

The crystallization kinetics and morphology of CaCO₃ crystals precipitated from the high salinity oilfield water were studied. The crystallization kinetics measurements show that nucleation and nuclei growth obey the first order reaction kinetics. The induction period of precipitation is extended in the high salinity solutions. Morphological studies show that impurity ions remain mostly in the solution phase instead of filling the CaCO₃ crystal lattice. The morphology of CaCO₃ precipitates can be changed from a smooth surface (calcite) to rough spheres (vaterite), and spindle rod bundles, or spherical, ellipsoid, flowers, plates and other shapes (aragonite).

The IR spectra of aqueous solutions of sodium chloride and rubidium chloride with the same concentration of 0.1 M upon freezing are studied in the middle IR region. The changes that occur in the absorption bands of the bending ν₂, compound ν₂ + ν_L, and stretching (ν₁, 2ν₂, and ν₃) vibrations of water molecules with gradual crystallization of the solutions are studied. The obtained spectra of crystallized solutions are compared to the IR spectrum of ice Ih. Analysis allows conclusions about the structure of the investigated frozen crystallized solutions.

Lead–magnesium hydroxyapatite solid solutions Pb_(10–x)Mg_x(PO₄)₆(OH)₂ have been prepared via a hydrothermal process. They were characterized by X-ray powder diffraction, Transmission Electron Microscopy (TEM), chemical and IR spectroscopic analyses. The results of the structural refinement indicated that the limits of lead-magnesium solid solutions (x ≤ 1.5), a regular decrease of the lattice constant a and a preferential magnesium distribution in site S(I). Through the progressive replacement of Pb²⁺ (r = 0.133 nm) by the smaller cation Mg²⁺ (r = 0.072 nm), all interatomic distances decrease in accordance with the decrease of the cell parameters. According to what could be expected from the coordinance of the metallic sites S(I) (hexacoordination) and S(II) (heptacoordination), the small magnesium cation preferentially occupies the four sites S(I). The results of the TEM analysis confirm the presence of magnesium in the starting solution and reveals the decrease in the average size of crystals. The IR spectra show the presence of the absorption bands characteristic for the apatite structure.

Water-soluble forms of a hydrophobic dye, zinc tetraphenylporphyrinate, are obtained via its solubilization by polymer particles of the micellar type formed by a copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate. Hydrodynamic radii R_h and the size distribution of such particles in neutral aqueous buffer solutions are determined via dynamic light scattering. The electrochemical activity of the encapsulated dye is found, and its photochemical properties (absorption and fluorescence) are studied.

The composite containing reduced graphene oxide and MnO nanoparticles (RGO/MnO) has been prepared via a one step pyrolysis method. The MnO nanoparticles were uniformly dispersed on the surface of RGO nanosheets forming MnO/RGO composite. The composite displays a maximum absorption of ‒38.9 dB at 13.5 GHz and the bandwidth of reflection loss corresponding to –10 dB can reach 4.9 GHz (from 11.5 to 16.4 GHz) with a coating layer thickness of only 2 mm. Therefore, the obtained RGO/MnO composite a perfect lightweight and high-performance electromagnetic wave absorbent.

The surface properties of ultradisperse polytetrafluoroethylene coatings on polyethylene terephthalate materials modified in a supercritical carbon dioxide medium with co-solvent additions (aliphatic alcohols) were analyzed. An atomic force microscopy study revealed the peculiarities of the morphology of the hydrophobic coatings formed in the presence of co-solvents. The contribution of the co-solvents to the formation of the surface layer with a low surface energy was evaluated from the surface energy components of the modified polyester material. The stability of the coatings against dry friction was analyzed.

The sorption of triangular silver nanoplates on polyurethane foam is investigated as a procedure for creating a nanocomposite sensing material for subsequent use in optical means of chemical analysis. Triangular silver nanoplates are synthesized and characterized, and a simple sorption technique for the formation of a composite material based on these nanoplates is proposed.

Materials are produced with porous layers based on ethanolamine derivatives of PVC or compounds of active carbon with hydroxyethylcyclam derivatives of PVC with aqua complexes of chloride hydrogen cross-linked with the surface of cellulose or asbestos fabric. Their capacity for sorption with respect to hexane and benzene in the saturated vapor and liquid phases is determined. The dependences of current on voltage in a circuit are determined for bridges composed of these materials in air, and in the vapor and liquid phases of benzene and hexane between 3 M HCl solutions and 3 M HCl solutions containing 3 M CaCl₂. It is established that only H⁺ ions migrate along the bridges between the HCl solutions, and H⁺ and Cl^– ions were the only species that moved along the bridges between the HCl solutions containing CaCl₂. The voltages at which the movement of ions starts are determined, and constants characterizing the conductivity of the layers are found. It is shown that these parameters depend on the structure of a layer, the nature of the fabric, and the medium surrounding a bridge.

The anticoagulant activity of high-molecular-weight heparin is increased by developing a new highly active heparin complex with glutamate using the thermodynamic model of chemical equilibria based on pH-metric data. The anticoagulant activity of the developed complexes is estimated in the pH range of blood plasma according to the drop in the calculated equilibrium Ca²⁺ concentration associated with the formation of mixed ligand complexes of Ca²⁺ ions, heparin (Na₄hep), and glutamate (H₂Glu). A thermodynamic model is calculated by mathematically modelling chemical equilibria in the CaCl₂–Na₄hep–H₂Glu–H₂O–NaCl system in the pH range of 2.30 ≤ pH ≤ 10.50 in diluted saline that acts as a background electrolyte (0.154 М NaCl) at 37°C and initial concentrations of the main components of ν × 10⁻³ M, where n ≤ 4. The thermodynamic model is used to determine the main complex of the monomeric unit of heparin with glutamate (HhepGlu^5–) and the most stable mixed ligand complex of Ca²⁺ with heparin and glutamate (Ca₂hepGlu^2–) in the pH range of blood plasma (6.80 ≤ рН ≤ 7.40). It is concluded that the Ca₂hepGlu^2– complex reduces the Ca²⁺ concentration 107 times more than the Ca²⁺ complex with pure heparin. The anticoagulant effect of the developed HhepGlu^5– complex is confirmed in vitro and in vivo via coagulation tests on the blood plasma of laboratory rats. Additional antithrombotic properties of the developed complex are identified. The new highly active anticoagulant, HhepGlu^5– complex with additional antithrombotic properties, is patented.

A version of a measuring system whose advantages include multifunctionality, simplicity, and availability of the main components is proposed. The system is built from relatively inexpensive digital multimeters, a programmed temperature controller, and a power source interfaced to a PC. It is shown that the developed software allows synchronous visualization in real time on a monitor and the accumulation of arrays of data on a series of kinetic dependences in the processes of thermally stimulated luminescence and electroluminescence.

The effect of urea on the thermodynamics of hexadecyltrimethylammonium bromide (CTAB) micelle formation in aqueous urea solutions was studied by isothermal titration microcalorimetry. The thermodynamic functions of ΔH, ΔG, and ΔS of CTAB micelle formation were calculated. The critical micelle concentrations (CMC) were determined. The addition of urea to the solution decreased the micelle formation entropy. This was attributed to the “lowering” of the structural temperature of the solution, which led to an increased number of hydrogen bonds and structure formation of water.

The list of authors and their affiliations should read:

N. V. Root^{a, b}, D. Yu. Kultin^a, L. M. Kustov^{a, b}, I. K. Kudryavtsev^a, and O. K. Lebedeva^a,*

^aDepartment of Chemistry, Moscow State University, Moscow, 119991 Russia

^bN.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Russia

*e-mail: lebedeva@general.chem.msu.ru